What could hard light be?

Question

For this question, I'm using the magic system discussed here that I will sum up with this: you take energy from your environment (e.g. heat from the atmosphere) and transform it into another form to cast a variety of spells. The spell itself must be either pure energy or resulting from said energy.

One particular spell is hard light, which is the purpose of this question. However, I'm having a hard time determining how I could generate hard light in compliance with the rules of my universe.

So here is what hard light is and isn't:

• It is solid. Not necessarily in the physical sense of the word, but hard light collides with any physical object, include other hard light objects.
• It glows. It generates faint light (as opposed to reflecting it).
• It is cold. It isn't a freezing hazard though.
• It does block what a wall would block. Besides, physical objects, this includes energy, e.g. heat.
• It doesn't block what a wall wouldn't block. E.g. radio signals.
• It only causes blunt force trauma, much unlike a light saber.
• It is a constant-cast spell. If the caster stops casting, hard light dissipates. Ideally, does not persist, though it could take a few seconds to dissipate.
• It is moderately translucent, as in opaque glass translucent.
• It is not a block of ice. That would be just too easy.
• It is not solid light, unless solid light actually exists and would meet other requirements.

I've noted in italic requirements you can play with if you have to.

The rules of magic here are:

• Assume magic always works as advertised.
• Assume the caster is not hurt by their spells.
• Assume there is always just the right amount of energy to do what you want to do.
• You can only transform energy. As such, a spell is energy, a discharge of energy or anything energy-related.
• Outside of the aforementioned magic, assume rules of physics apply.

Given all that, what could be the physical nature of hard light?

Answer 1

Hard light could be pseudo-matter made up of 'virtual atoms' - electron shells without a nucleus. This could be done by controlling electromagnetic fields. Such material could simulate most properties of matter, such as specific heat, hardness, and transparency, but would be almost massless.

Things glow when their electrons drop to a lowered energy state. Presumably keeping the electrons in place requires a constant input of magical energy; when you funnel too much energy into the construct by accident you need to radiate it off as light to keep the construct from dissipating. Perhaps the glow of such a construct could indicate the fine control skill of the mage creating it; glow implies wasted energy (this will be the case no matter how you explain it). A truly skilled construct will have a glassy appearance with very little glow, but even a talented mage might have difficulty controlling their output when they are forced to channel more energy than they are accustomed to.

The construct could be as cold or as hot as you like, but cold implies that the virtual atoms are held firmly in place and the construct is stable, while heat suggests that it is starting to break up.

Answer 2

If I can take the liberty of turning 'it radiates cold', which doesn't make thermodynamic sense (coldness isn't a physical property, just the absence of heat, which is), into 'it absorbs heat', which is presumably what you mean anyway.

Postulating hard light as a 'portal' with a membrane that only allows massless particles through. Or glass or somesuch, which allows you to set how translucent it is. Then further saying that it has a dim light source at the centre. In other words, so far it's a light source created from transdimensional photons with a translucent pane. This makes everything except for the heat bit work.

So, to fix this: have the membrane full of micropores. Say, slightly bigger than a water droplet (adjust to taste), then have a vacuum of the extremely cold outer space variety between the transdimensional light source and the membrane. Things like hot air currents etc. would get absorbed by this. The only issue left would be infra-red radiation, which could be solved, if desired, by the light source being a crystal that absorbs infra-red frequencies (condensed matter physics allows this). When I say 'absorb', I mean a reverse Unbestanum process. Precise regulation of number of micropores and heat of the source would hopefully be enough to not freeze things and for reasonable pressure regulation. Previously warm molecules then come out again as cold molecules having lost energy, which also helps prevent pressure issues.

Edit:

To clarify, the cooling by convection doesn't work because the vacuum is cold, but because it is a vacuum: relatively small pressure inside causes any particles that fit through the micropores to go through and get absorbed by the reverse Unbestanum process. This includes warm air molecules. As already mentioned, these then get emitted as cold molecules, which also allows for finer control of the temperature and pressure.

Also worth mentioning is that when the process of constant molecule absorption stops, the membrane will automatically collapse inwards.

Answer 3

Your rules preclude your simply conjuring up matter where there was before. However, it doesn't have to have anything to do with light/photons; it might be called that because of its appearance.

Maybe you can cause the gas and any suspended dust particles to be locked in place. Air would be as solid as a wall if you couldn't move past it as it doesn't flow around you.

It's cold because the continuing spell prevents molecules from moving: thermal energy transferred to it would normally make the molecules move faster, and the spell dampens that. Thus, it serves as a cold sink, which constantly drains the spell.

For whatever reason it's cold, you can run a sterling engine off of it, thus it's a source of power. I expect this will require energy to keep it going and/or make it run out.

Answer 4

So the spell has to be pure energy or the result of a pure energy event.

Scientifically we've been able to slow light down to a crawl and even stop it.
Using a pure energy magical field you could make the same effect, manipulating energy in an area to the point that light almost stops, though some does pass through and out of the field eventually which causes a glow.

The one problem is the blunt force trauma part, since photons are massless, and even held together in a field may behave more like a gas than a solid. However if the magical field is slowing down an area of spacetime enough to slow light, it might effect the other things in the area equally, so solidified reality.

Also you can say that once the field is established that it's self contained and while air can flow around it, anything solid like a wall, head, etc. would be excluded from the area until the casting stops.

Another possible idea is if you started the field inside of a solid object, so that the field would anchor the object to reality. Could be used as climbing anchors that don't leave marks once the spell finishes, or to seal a door so there is no way to open it as long as the spell is working.

Answer 5

I take it you want a plausible "physical" explanation for what the magic does, while keeping the magic magical. Kindof like how all of Superman's powers can be explained by an ability to change the momentum of matter.

In the case of hard light, we could propose that magic is changing the vacuum energy in nearby space. The energy of the vacuum is increased and then guided into a spontaneous symmetry breaking. We get a new vacuum state where the Higgs field now couples to the photons, giving them mass. This vacuum, having a higher energy than our normal vacuum, is unstable and decays into normal vacuum when the magic is paused or the light travels outside the magicians's sphere of influence.

Scientifically speaking, the magician is creating a local false vacuum. Simply speaking, the laws of nature have changed in some small area around the magician.

WARNING: Care should be taken when altering the vacuum. If a vacuum with a lower energy state is created, it can cause a cascade effect where the rest of our universe drops into the same low vacuum state. The laws of nature in this new vacuum can be very different from our own. There may even exist vacuum states where (gasp!) magic no longer works!